The analysis of body fluids allows an early and reliable detection of pathological conditions in clinical diagnostics and the specific and fact-based monitoring of physical conditions. More recently, the amount of blood required for individual analyses directed specifically towards one parameter is often only a few microliters to less than one microliter. For blood collection, skin, and in particular the finger pad or the earlobe of the person to be examined, is usually pierced with the aid of a sterile and sharp lancet. This method is particularly suitable when the blood sample can be analyzed immediately after it is collected.
Carrier-bound rapid tests have become established for chemical and biochemical analysis of body fluids in laboratories specialized for this purpose and are also used outside permanent laboratories. Such carrier-bound rapid tests based on specially developed dry chemistry can be carried out simply and with ease even by a layperson despite often complex reactions involving sensitive reagents. Common examples of carrier-bound rapid test devices are test strips used by diabetics for determining blood glucose concentration.
Analytical test elements for carrier-bound rapid tests typically comprise an application site on which the body fluid to be analyzed is applied and a detection area in which the particular analyte is detected. These strips are usually configured such that the sample is applied on top of and directly to the application area, in which case the application site lies above the detection area and the two areas may be separated by a fleece or the like. Alternatively, in the case of test strips having a capillary channel, the detection area is displaced relative to the application site, typically along the longitudinal axis of the test strip. This assembly has the advantage that the test element can be positioned in such a manner that the application site is situated in a readily accessible position outside of a measuring instrument, whereas the detection area is located inside the instrument. The evaluation unit is also located inside the instrument in a well-protected position next to the detection area. The test strip can remain in one position during the entire concentration determination and does not have to be moved into a measuring position after application of the sample. In the case of test strips that utilize capillary action to transport the sample, the sample is transported from the application site to the detection area by a transport element such as a capillary, absorbent fabric, or fleece that generates capillary action.
In the case of analytical test elements, and in particular those test strips providing a capillary action that are classified as “self-dosing,” there is frequently an excess amount of blood at the site of application or on the outer sides or edges of the entrance to the capillary space after the measurement. The required handling to dispose of such a contaminated test strip is, on the one hand, not user-friendly and unhygienic, and, on the other hand, represents a contamination risk, especially in hospitals.
A similar hygiene problem arises when test elements are stored in a magazine and the magazine is inserted into a measuring instrument. Before the measurement, a test strip is moved by the instrument into an application position and after the measurement, the used test strip is returned back into the magazine and stored. This provides an advantage for the user such that she does not have to dispose of a test strip after each test. Once all test strips in the magazine are used, the magazine is removed from the measuring device and replaced by a new magazine. The used test elements are stored in the magazine and can therefore be hygienically handled and disposed of. A disadvantage of these systems is that, although the test strips are stored and sealed in the magazine before use to protect them from dirt and moisture, the individual storage chambers for the test strips are usually no longer closed and sealed after use. Thus, an excess amount of applied blood, which remains adhered to the used test strips, can crumble off over time and contaminate the instrument and, in particular, the evaluation optics or other instrument components through openings in the magazine.
U.S. Pat. No. 5,104,640 describes an adhesive agent used for blood on glass supports. In this case, polyvinyl pyrrolidone (PVP) is used as an additive in the alcohol fixation of blood smears. In the case of blood smears, blood is applied, smeared, and examined on a glass support (i.e., the site of application and the detection area are at the same site). The sample is spread as thinly as possible, because the blood substantially adheres to the glass support by adhesion forces without the use of an adhesive agent. PVP only supports this effect and, in this case, only has to adhere to a thin layer of blood.